Magnetic proximity switch



March 24, 1970 R. w. BLAIN 3,503,020

MAGNETIC PROXIMITY SWITCH Filed Sept. 20, 1967 2 Sheets-Sheet 1 INVENTOR. 28 5 ROY w. BLAIN -7- BY F I G 3 ATTORNEY March 2 4, 1970 R. w. LAlN 3,503,020

MAGNETIC PROXIMITY SWITCH Filed Sept. 20, 1967 2 Sheets-Sheet 2 so as 32 I4 ea 14 INVENTOR.

ROY W. BLAIN ATTORNEY United States Patent US. Cl. 335205 11 Claims ABSTRACT OF THE DISCLOSURE A magnetic proximity switch in which the movement of a bar magnet, afiixed to one end of a pivotally mounted arm, responsive to the presence of magnetically attractive masses passing in its vicinity opens and closes electrical contacts.

This invention relates to magnetic proximity switches in which a symmetrically magnetized permanent bar magnet is afiixed to one end of a pivotally mounted arm and carries that arm with it as it moves responsive to the closest magnetically attractive mass.

The magnetic proximity switch of this invention enjoys particularly utility when used in connection with automatic elevator systems. When so employed the switch of this invention is mounted either on the elevator or on the wall of the elevator shaft and is actuated by relative movement between the switch and a steel vane which passes close to the bar magnet as the elevator moves. For example, when this magnetic proximity switch is mounted on an elevator, the steel actuating vane is mounted on the shaft at a stationary point. As the elevator moves past the point where the steel vane is located the presence of the vane causes the bar magnnet to move towards it, thus actuating the electrical contacts in the switch.

Considerable difiiculty had previously been experienced in obtaining accurate, rapid, and predictable operating characteristics in magnetic proximity switches used in automatic elevator systems. In general tolerances on prior magnetic proximity switches were quite critical so that precise positioning of the switch relative to the actuating magnetically attractive mass was necessary.

The magnetic proximity switch of this invention is normally retained in its inactivated configuration by the attraction of the bar magnet for a ferrous plate which is mounted adjacent to and spaced a predetermined distance from the rear of the bar magnet. The bar magnet is symmetrically magnetized so that the presence of a magnetically attractive mass on the front side of the switch, at a distance from the magnet which is less than the distance between the magnet and the fixed ferrous plate on its rear wall, will cause the magnet to move towards its front side, thus placing the switch in its actuated configuration. As soon as the magnetically attractive mass moves away from the front of the magnet to a distance greater than the distance between the magnet and the ferrous plate behind it, the magnet will be drawn back toward the ferrous plate, thus bringing the switch into its inactivated configuration.

The spacing between the magnet and the fixed ferrous plate behind it is adjusted so that this distance is several times greater than the distance through which the magnet travels in moving from the inactivated to the activated position. Because of this spacing the attractive force between the magnet and the ferrous plate behind it is substantially the same in either the activated or inactivated configuration. This increases the responsiveness of the switch in that there is a very short delay time between the removal of the magnetically attractive mass from the front of the switch and its return to the activated position. The light weight of the bar magnet also enhances the speed with which the switch responds to the presence of a magnetically attractive mass. The symmetrical magnetization of the bar magnet automatically compensates for any changes in its magnetic properties while in service. The light weight of this bar magnet and the attendant mechanism cause substantially noiseless operation of the switch which avoids disturbing the occupants of the elevator by an audible thump as the switch moves from an inactivated to an activated configuration.

Reference is made to the accompanying drawings in which:

FIGURE 1 is a top plan view of the magnetic proximity switch with the cover removed;

FIGURE 2 is a top plan view of the arm and bar magnet used in the proximity switch;

FIGURE 3 is a cross-sectional elevation taken along line 33 in FIGURE 2;

FIGURE 4 is a cross-sectional elevation taken along line 44 in FIGURE 1 showing the magnetic proximity switch in its normal or inactivated configuration;

FIGURE 5 is a cross-sectional view similar to that shown in FIGURE 4 with the proximity in its activated configuration;

FIGURE 6 is a cross-sectional elevation taken along line 6-6 in FIGURE 1;

FIGURE 7 is a cross-sectional elevation taken along line 7-7 in FIGURE 1; and

FIGURE 8 is a cross-sectional elevation taken along line 88 in FIGURE 1.

Referring particularly to the drawings there is illustrated a magnetic proximity switch 10 which includes a housing 12 having a first side 14 which in operation is provided with a cover not shown. Housing 14 includes a second side 16, a first end 18, and a second end 20. Pivot arm 22 is mounted on a pivotal mounting 24 which includes pin 26 slidably engaged in sleeve 28. Magnet 30 is held at the end of pivot arm 22 which is remote from pivotal mounting 24 by retainer block 32 which is secured to pivot arm 22 by fastener 33. Electrical .contacts are actuated by the movement of pivot arm 22; A first set of electrical contacts is indicated generally at 34 and includes first contact 36 which is mounted on the outward end of first contact spring arm 38, secondcontact 40 which is mounted on the outward end of second contact spring arm 42, third contact 44 which is mounted on the outward end of third contact spring arm 46, and fourth contact 47 which is mounted on second contact spring arm 42 in operative relationship with third. contact 44. First set of electrical contacts 34 is controlled by the movement of first contact actuating cam 48 with pivot arm 22. The location of first contact actuating cam 48 with respect to first set of electrical contacts 34 is regulated by adjustment screw 49 which is mounted in retainer block 32. A second set of electrical contacts is indicated generally at 50 and includes a fifth contact 52 which is mounted on the outward end of fifth contact spring arm 54, sixth contact 56 which is mounted on the outward end of sixth contact spring arm 58, seventh contact 60 which is mounted on the outward end of seventh contact spring arm 62, and eighth contact 63 which is mounted on the outward end of sixth contact spring arm 58 for operative engagement with seventh contact 60. Second set of electrical contacts 50 is made responsive to the movement of pivot arm 22 by means of second contact actuating cam 67. The position of second contact actu-ating cam 67 relative to pivot arm 22 is regulated by adjustment screw 65 which is mounted in retainer block 32.

A magnetically attractive mass 64 is afiixed to second 3 side 16 of housing 12 at a predetermined distance from magnet 30'.

The movement of pivot arm 22 is limited by path travel adjustment screw 66 which carries spacer 68. As illustrated particularly in FIGURE 6 spacer 68 limits the travel of pivot arm 22 by providing stops on either side of pivot arm 22 which contact annular elastic shock absorber 72. Screw 66 and spacer 68 are secured together by nut 70. The movement of pivot arm 22 is limited to the distance between the abutting flanges on spacer 68 and shock absorber 72. v

The distance between magnet 30 and magnetically attractive mass 64 in the normal or inactuated position is illustrated at 74-74 in FIGURE 4. The distance between magnet 30 and magnetically attractive mass 64 in the actuated position is illustrated at 76-76 in FIGURE 5. The position of shock absorber 72 in the normal configuration is illustrated at 78-78 in FIGURE 6, and the position of shock absorber 72 in the actuated configuration is illustrated at 80-80 in the same figure.

The moving mechanism inside housing 12 is carried by mechanism support member 82 which is positioned in housing 12 by the presence of locator projections 84. Mechanism support member 82 is secured to housing 12 by screw 86. Mechanism support member 82 supports pin 26 which carries pivot arm 22, as well as serving as a mount for the contact spring arms and suitable electrical connections. Mechanism support member 82 is made of non-conductive material in which are mounted first, second and third electrical connections 88, 90, and 92, respectively. Housing 12 is provided with threaded receptacles 94 which are adapted to receive the screws which secure the cover, not shown, on housing 12. Openings 96, 98, and 100, respectively, provide convenient mounting and access ports when the cover is secured in position on housing 12. One or more electrical conduits may be received in these openings.

In operation magnetic proximity switch 10 is normally mounted so that pivot arm 22 extends vertically and magnet 30 is either above or below pivotal mounting 24. Housing 12 is positioned so that a steel vane or other magnetically attractive mass passes by the first side 14 at a distance from magnet 30 which is less than distance 74-74. Distance 74-74 is a predetermined distance which is regulated by the height of pillar 102. Because of the symmetrical magnetization of magnet 30 distance 74-74 may be varied considerably without adversely influencing the characteristics of the switch. In one embodiment distance 74-74 has been set at /s of one inch. In

general the predetermined distance 74-74 should be at least four times the length of the path traveled by magnet 30, and preferably at least about eight times the length of such path.

As will be understood by those skilled in the art what has been described are preferred embodiments which modifications and changes may be made without departing from the scope and spirit of the accompanying claims.

What is claimed is:

1. A magnetic proximity switch comprising:

a symmetrically magnetized elongated bar magnet having first and second sides and being mounted for movement in a direction transverse to its longitudinal axis along a reciprocal path from a normal position to an actuated position, an elongated magnetically attractive static mass in alignment with said path, said static mass having the longitudinal axis thereof substantially parallel to the longitudinal axis of the bar magnet and having a fixed position adjacent to and spaced at a predetermined distance from said bar magnet on said second side when said magnet is in said normal position, whereby said magnet and said mass have a condition of mutual attraction to retain said magnet in said normal position, electrical contact means responsive to the movement of said magnet; said magnet being movable from said normal to said actuated position, said movement being in response to the presence of a magnetically attractive actuating mass approaching said first side of said magnet to a location in said path wherein the distance from said magnet to said actuating mass is less than said predetermined distance.

2. The magnetic proximity switch of claim 1 wherein the length of said predetermined distance is several times greater than the distance from said magnet to said actuating mass when said actuating mass is in said path.

3. The magnetic proximity switch of claim 1 wherein said magnet is aflixed to one end of a pivot arm, the other end of said arm being pivotally mounted.

4. The magnetic proximity switch of claim 1 wherein said predetermined distance is at least about eight times the distance from said magnet to said actuating mass when said actuating mass is in said path.

5. The magnetic proximity switch of claim 1 wherein said mass comprises a ferrous plate.

6. The magnetic proximity switch of claim 1 wherein said predetermined distance is at least four times the distance from said magnet to said actuating mass when said actuating mass is in said path.

7. The magnetic proximity switch of claim 1 wherein said magnet is a cylindrical rod.

8. A magnetic proximity switch as in claim 1 wherein respective ends of said magnetically attractive static mass are substantially equidistant from corresponding ends of said bar magnet and all portions of said elongated bar magnet are adapted to move at equal rates away from and toward corresponding portions of said magnetically attractive static mass in response respectively to presence and absence of said magnetically attractive actuating mass relative to a position in said path on said first side of said magnet.

9. A magnetic proximity switch as in claim 1 wherein said bar magnet in all operative positions has a location in said path interposed between said magnetically attractive static mass and the position occupied by said actuating mass when in alignment with said path.

10. A magnetic proximity switch as in claim 1 wherein there is a housing, and an arm pivotally mounted at one end on said housing, the other end of the arm having the bar magnet mounted thereon, transversely with respect to the longitudinal axis of said arm.

11. A magnetic proximity switch as in claim 10 Wherein there is motion restricting means acting between the housing and the arm whereby to limit movement of the arm in both directions to a small fraction of said distance.

References Cited UNITED STATES PATENTS 5/1941 ,Marchant 335-205 10/1966 Blumish 335-207 US. Cl. X.R. 200-47 

